Nikon 24-70 2.8 manual focus issue

My brand new lens makes a significant (I say significant but its not grindy, or deafening, just...signifigcant!) 'ratchet' sound ONLY when manually focusing, compared to my 70-200mm which only makes a soft whisper noise. I can only assume there is a minor fault (I say minor as the lens is pin sharp and focuses quickly). I've researched the issue - but can't seem to find a lot of info about this particular problem (although some people have reported it).

The people who have the combo 24-70 and 70-200 - is there a difference in the manual focus noise?
Secondly and much less important:

The 24-70 lens also seems to bit ever so slightly stiffer to zoom at either end of the range, and easier to zoom aounf the 50mm mark - is this normal too?

I feel like I'm being very fussy but it was hard spending this much money on a lens and I want to make sure I have a lens with the build quality it's alleged to have.
Thanks for your help in advance
Sam